Generally, as cooling methods for information processing systems, a cooling technology which cools electric apparatuses in an information processing system by installing a plurality of cooling fans in a redundant configuration within the information processing system is well known.
For example, Japanese Patent Application Laid-Open No. 2001-68881 discloses plural cooling fans located in an electronic apparatus. In a normal status, some of the cooling fans are set in an operating state. And in an abnormal status, additional cooling fans in the electronic apparatus are shifted into an operating state. As a result, it is possible to guarantee the normal operation of the electronic apparatus.
Further, Japanese Patent Application Laid-Open No. 2005-57119 discloses a technology in which the amount of the wind produced by plural fans is controlled according to the detection result in detecting the status of at least one fan out of the fans.
In the above-mentioned cooling fans with a redundant configuration (for example, dual-type cooling fans or push-pull-type cooling fans), the co-rotation phenomena may occur in which, in the case of a failure of a cooling fan, the cooling fan are forced to rotate improperly by the force of the wind produced by other cooling fans.
Next, description will be made in more detail about the co-rotation phenomena in dual-type cooling fans and push-pull-type cooling fans as examples.
As shown in FIG. 10, in case of push-pull-type cooling fans, cooling air is inhaled into a unit by a cooling fan 10-1.
It cools the inside of the unit, and then the cooling air heated as a result of such cooling is dragged toward a cooling fan 10-2, and is exhaled compulsorily to the outside of the unit.
On the other hand, in case of dual-type cooling fans as shown in FIG. 11, cooling air is inhaled by a cooling fan 11-1 and internal air is pressed to the outside by a cooling fan 11-2 compulsorily.
In both of the push-pull type cooling fans and the dual-type cooling fans, the inhalation and exhalation are done in a two-stage configuration, and a fan at the former stage and a fan at the latter stage mutually influence each other.
Considering the case of the dual-type cooling fans as an example, even if a failure occurs on a cooling fan and it is no more possible to rotate by itself, the failed cooling fan may rotate due to air flow caused by the rotation of the other cooling fan (the co-rotation phenomena).
When the above-mentioned co-rotation happens, if the threshold rotation rate of cooling fans for detection of a fan failure is set to a low value and a failed cooling fan rotates faster than the threshold rotation rate because of the co-rotation phenomena, it is difficult to detect the failure of the failed fan.
As the result, a problem mentioned below is caused. That is, even though the redundant configuration no more functions adequately, the operation of the system continues and the system may stop suddenly without any caution in advance.
On the other hand, when the threshold rotation rate of cooling fans is set to a high value, the failure detection becomes too sensitive, and the variation of the rotation rates of individual cooling fans get to be unable to be ignored.
That is, even if a cooling fan is not failed but its rotation rate temporarily declines, there is a problem that the normal cooling fan is detected as a failed fan erroneously and a unnecessary log, alarm or the like is generated, requesting maintenance and causing unnecessary maintenance.
The object of the present invention is to provide a failure diagnosis system for cooling fans, a failure diagnosis device for cooling fans, a failure diagnosis method for cooling fans, a computer readable medium therefor and a cooling device, which detect a failure of cooling fans even at the time of occurrence of the co-rotation phenomena.